We have developed procedures to isolate cells from the microvessels of the rabbit marginal vascular network, from the dermis of the newborn foreskin, and from adult facial skin. The factors that control the proliferation and formation of blood vessels from the microvasculature and from the macrovasculature are being studied. The relationship of 6 nm and 10 nm filaments to changes in endothelial cell architecture is being analyzed by both electron microscopy and by SDS gel electrophoresis.